The present invention relates to novel PVC plastisols comprising effect pigments. The present invention also relates to a new process for preparing PVC plastisols comprising effect pigments. The present invention further relates to the use of the novel PVC plastisols comprising effect pigments and of the PVC plastisols comprising effect pigments prepared by the novel process in coil coating for producing effect coatings and also color and effect coatings.
PVC plastisols are colloidal dispersions of polyvinyl chloride (PVC) prepared by emulsion or microemulsion polymerization in plasticizers. When the PVC plastisols are heated the plasticizers diffuse into the dispersed polymer particles, where they lodge between the macromolecules and hence produce plasticization of the PVC plastisols. After cooling, highly elastic, abrasion-resistant, and dimensionally stable coatings are obtained.
In automotive OEM finishing PVC plastisols further comprising pigments, fillers, and heat stabilizers are used as additional coatings to counter mechanical damage and corrosion in areas of particular risk of stone chipping (underbody, wheel arches) and for sealing weld seams (seam sealing). Application is normally manual or via special spraying techniques. The temperatures of curing (gelling) are generally situated between 140 and 180° C.
(Cf. Römpp Online, Georg Thieme Verlag, Stuttgart, N.Y. 2003, “PVC plastisols”).
PVC plastisols comprising effect pigments, such as platelet-shaped aluminum effect pigments or interference pigments, are known per se. They normally comprise a standard PVC paste resin and a PVC extender resin. The known PVC plastisols comprising effect pigments are suitable for coil coating.
Coil coating is a special form of the roll coating (Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, N.Y., 1998, page 617, “roll coating”) and, occasionally, of the spray coating and flow coating of metal strips (“coils”) with liquid coating materials. It is a continuous process: all worksteps, such as cleaning, pretreatment, coating, and curing, etc., are carried out in one operation on one line. Schematically, coil coating embraces the following steps: cleaning and degreasing of the coil are followed by a multistage chemical pretreatment with subsequent passivation, rinsing and drying. The coils used are in particular of steel, such as galvanized steel, or aluminum. Cooling of the coils is followed by application of the liquid coating material to one or both sides using two or three rolls, usually by the reverse roller-coating method. After a very short evaporation time the film applied is cured thermally at temperatures from 180 to 260° C. for 20 to 60 s. Where a multicoat paint system is being produced, application and cure are repeated. The speeds of coil coating of lines are up to 250 m/min (Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, N.Y., 1998, page 55, “coil coating”).
Since the processing of the metal does not take place until after the coating operation, the resultant coatings need to have extremely high mechanical integrity. The coated coils are used customarily in the architectural sector for producing ceiling and wall elements, doors, pipe insulation, roller shutters or window profiles, in the vehicle sector for producing paneling for caravans or truck bodies, and in the household sector for producing profile elements for washing machines, dishwashers, freezers, ice boxes or ranges (cf. Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, N.Y., 1998, “coil coating”, page 55, and “coil coating materials”, page 116).
In the coatings produced from the known PVC plastisols comprising platelet-shaped effect pigments, however, the platelet-shaped effect pigments are not oriented predominantly or exclusively parallel to the surface of the coatings, with the consequence that the desired optical effect of the platelet-shaped effect pigments does not come about in the coatings, or not to the required extent. Thus with platelet-shaped aluminum effect pigments, for example, only coatings with glitter effects can be produced, but not coatings exhibiting a strong color flop or light/dark flop, such as is characteristic of high-grade metallic paint systems.
The use of PVC plastisols comprising effect pigments and of the inherently advantageous coil coating process for producing high-grade effect coatings, or color and effect coatings, for automotive OEM finishing has therefore been unsuccessful to date essentially owing to the fact that the existing coatings comprising effect pigments even prior to deformation do not have the required automobile quality. In particular it is not possible to reproduce the shades and optical effects the automobile industry requires, or the required gloss and overall appearance.